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Chelation and stabilization of berkelium in oxidation state +IV


Berkelium (Bk) has been predicted to be the only transplutonium element able to exhibit both +III and +IV oxidation states in solution, but evidence of a stable oxidized Bk chelate has so far remained elusive. Here we describe the stabilization of the heaviest 4+ ion of the periodic table, under mild aqueous conditions, using a siderophore derivative. The resulting Bk(IV) complex exhibits luminescence via sensitization through an intramolecular antenna effect. This neutral Bk(IV) coordination compound is not sequestered by the protein siderocalin—a mammalian metal transporter—in contrast to the negatively charged species obtained with neighbouring trivalent actinides americium, curium and californium (Cf). The corresponding Cf(III)–ligand–protein ternary adduct was characterized by X-ray diffraction analysis. Combined with theoretical predictions, these data add significant insight to the field of transplutonium chemistry, and may lead to innovative Bk separation and purification processes.

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Figure 1: Stabilization and sensitization of Bk(IV) were achieved through chelation with a siderophore derivative.
Figure 2: Mass spectrometry provided definitive evidence of the oxidation state +IV for the Bk species formed with ligand 1.
Figure 3: The selectivity of Scn toward [M(III)1] complexes and the different polarity of [M(IV)1] complexes can be used to discriminate Bk from other metal ions.

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This work was supported by the US Department of Energy (DoE), Office of Science Early Career Research Program and Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division at the Lawrence Berkeley National Laboratory under contract DE-AC02-05CH11231 (R.J.A.), by the National Institutes of Health (R01DK073462, R.K.S.), and by the Scientific Discovery through Advanced Computing (SciDAC) program of the US DoE, Office of Science, Office of Advanced Scientific Computing and Office of Basic Energy Sciences (W.A.d.J.). The Radiochemical Engineering and Development Center at Oak Ridge National Laboratory is supported by the US DoE, Isotope Development and Production for Research and Applications Program. The Advanced Light Source (ALS) and Energy Research Scientific Computing Center (NERSC) are supported by the Director, Office of Science, and Office of Basic Energy Sciences, of the US DoE under contract no. DE-AC02-05CH11231. The Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program provided an award of computer time through the Oak Ridge Leadership Computing Facility, a US DoE Office of Science User Facility supported under Contract DE-AC05-00OR22725. We thank M. Allaire, S. Morton, J. Bramble, K. Engle, M. Dupray, and I. Tadesse for assistance in implementing diffraction data collection on radioactive crystals at ALS 5.0.2 beamline.

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G.J.-P.D., M.S.-H., W.A.d.J., R.K.S., and R.J.A. designed the research. G.J.-P.D., M.S.-H., and M.-C.I. collected and analysed optical spectroscopy and mass spectrometry data. R.J.A. and D. D. A crystallized the protein–metal adducts. P.B.R., D.D.A., and C.Y.R. collected and analysed crystallographic data. P.B.R. and R.K.S. solved the structures. J.B. and W.A.d.J. performed theoretical computations. All of the authors discussed the results and commented on the manuscript.

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Correspondence to Wibe A. de Jong or Roland K. Strong or Rebecca J. Abergel.

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Deblonde, GP., Sturzbecher-Hoehne, M., Rupert, P. et al. Chelation and stabilization of berkelium in oxidation state +IV. Nature Chem 9, 843–849 (2017).

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